Fibroids are non-cancerous (benign) growths that develop in or around the uterus. They are made of muscle and fibrous tissue and can vary in size, from as small as a pea to as large as a melon. These tumors can develop in various parts of the uterus, including the inner lining (submucosal), the muscular wall (intramural), or on the outside of the uterus (subserosal).